The dramatic increase of the world market price for gold compared to other metals stimulated the semiconductor device industry to develop copper wire ball bonding as a replacement of gold wire ball bonding. While copper is a welcome bond wire material because it has about 30% higher electrical conductivity when compared to gold, use of copper bond wires requires the formation of intermetallics with aluminum bond pads for strong and reliable ball bonds. The need for the intermetallic formation necessitates the use of higher temperatures during the copper wire bonding process, when compared to the prior gold wire bonding processes. For copper wire ball bonding, temperatures above 220° C. and more typically in the range of about 250° C. are needed, while for gold, temperatures in the range of 180° C. are sufficient. At these higher process temperatures, the elasticity modulus of the adhesive polymeric materials used for the die attach layer between the back side of the semiconductor die and a substrate decreases, causing a risk of non-stick-on-pad (NSOP) defects. This NSOP issue can be affected with limited success by optimizing the curing profile of an adhesive polymeric material. If the modulus of the adhesive polymeric material is high at high temperatures, then the material may be at risk of delamination during stress tests. Such stress tests involve, for instance, repeated temperature cycles from −65° C. to +150° C., or 1000 hr storage at 85° C. and 85% relative humidity and while applying an electric bias to the packaged device.
While polymeric materials such as polyimides and epoxies are insulators, many integrated circuit device types require adhesive die attach materials that provide electrical and/or thermal conductivity. Consequently, many die attach materials, such as silver epoxy, include a metallic filler such as silver. In the electric field of a direct current (DC), for instance between an anodic die pad and a nearby cathodic bond pad, the silver filled epoxy can undergo dissolution in the presence of moisture, creating positive silver ions. In the presence of an adsorbed water layer acting as an electrolyte, the positive silver ions can migrate in the DC electric field from the anodic die pad to the cathodic bond pad, where the ions are reduced to pure silver and eventually form a dendrite tree that can cause an electrical short between anode and cathode. Improvements are therefore desirable.